The lies we tell are more convincing when we need to pee

David Cameron uses bladder control for focus, but it can also be used to inhibit the impulse to tell the truth

Francois Lenoir/Reuters

David Cameron’s full-bladder technique really does work – but perhaps not in a way that the UK prime minister intends. Before important speeches or negotiations, Cameron keeps his mind focused by refraining from micturating. The technique may be effective – but it also appears to help people to lie more convincingly.

Iris Blandón-Gitlin of California State University in Fullerton and her colleagues asked 22 students to complete a questionnaire on controversial social or moral issues. They were then interviewed by a panel, but instructed to lie about their opinions on two issues they felt strongly about. After completing the questionnaire, and 45 minutes before the interview, in what they were told was an unrelated task, half drank 700 ml of water and the other half 50 ml.

The interviewers detected lies less accurately among those with a full bladder. Subjects who needed to urinate showed fewer signs that they were lying and gave longer, more detailed answers than those who drank less.

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The findings build on work by Mirjam Tuk of Imperial College London, whose study in 2011 found that people with full bladders were better able to resist short-term impulses and make decisions that led to bigger rewards in the long run. These findings hinted that different activities requiring self-control share common mechanisms in the brain, and engaging in one type of control could enhance another.

Other research has suggested that we have a natural instinct to tell the truth which must be inhibited when we lie. Blandón-Gitlin was therefore interested to see whether the “inhibitory spillover effect” identified by Tuk would apply to deception.

Although we think of bladder control and other forms of impulse control as different, they involve common neural resources, says Blandón-Gitlin. “They’re subjectively different but in the brain they’re not. They’re not domain-specific. When you activate the inhibitory control network in one domain, the benefits spill over to other tasks.”

Blandón-Gitlin stresses that her study does not suggest that David Cameron would be more deceitful as a consequence of his full bladder technique. But she says that deception might be made easier using the approach – as long as the desire to urinate isn’t overwhelming. “If it’s just enough to keep you on edge, you might be able to focus and be a better liar,” she says.

Intriguingly, exerting different forms of self-control sequentially rather than simultaneously seems to have the opposite effect, depleting an individual’s powers of restraint. Tuk found that participants who are instructed to inhibit their emotions while watching a film eat fewer crisps during the film, but eat more if they get access to the crisps later.

Tuk says the new study doesn’t add much to our understanding of impulse control, but the results “provide an important confirmation of the hypothesis that bladder control impacts human behaviour”.

Aldert Vrij, an expert on lie detection at the University of Portsmouth, UK, says it’s premature to discuss the implications from one small study. Publishing research on how to make people better liars also raises ethical concerns, he adds.